1. Field of the Invention
The present invention relates to a MEMS apparatus that includes a substrate mounted thereon a microelectromechanical system (MEMS) that has a sensor or an actuator (mechanical drive mechanism), and an integrated circuit that drives the mechanical drive mechanism, and a method of manufacturing the MEMS apparatus.
2. Description of the Related Art
Higher functions and higher performance can easily be realized with MEMS apparatuses created using semiconductor manufacturing technologies. Today, sensors and actuators applied with various MEMS apparatuses are commercially produced, and functional systems are being offered. In view of stability of the functional systems and improvement of the MEMS apparatuses on mechanical characteristics, a highly hermetic packaging technology or a sealing technology that protects the MEMS apparatus from an external factor such as moisture, while maintaining a hollow structure of the MEMS apparatus, has become important.
A general method of hermetically sealing a semiconductor substrate is an anodic bonding. The anodic bonding is a method that overlaps a glass that includes mobile ions and a silicon wafer (or metal and the like), and then softens the glass side by heating the overlapped glass and silicon wafer. At the same time, an electric double layer is generated by applying a high negative voltage to the glass side and a high positive voltage to the silicon wafer side, thereby joining the glass and the silicon wafer by electrostatic attractive force.
For example, in JP-A H10-163505 (KOKAI), a semiconductor inertial sensor suitable for, for example, a capacitance type acceleration sensor and an angular velocity sensor, is disclosed. The semiconductor inertial sensor is made by joining a silicon wafer formed with movable electrodes (MEMS) and a glass substrate formed with concaves using the anodic bonding. In JP-A 2004-42248 (KOKAI), an optical scanner (MEMS structure) formed by carrying out the anodic bonding between a dielectric body and a glass substrate, and the anodic bonding between the dielectric body and a metal film is disclosed. Moreover, in Adit Decharat et al., Novel Room-Temperature Wafer-to-Wafer Attachment and Sealing of Cavities Using Cold Metal Welding, MEMS2007, pp. 411-414, a method of capping by providing concaves and convexes to a substrate mounted with the MEMS and to a cap material that protects the MEMS in advance, and fitting the respective concaves and the convexes is disclosed.
However, in general, in the anodic bonding, the glass and the silicon wafer should be heated up to approximately 500 degrees centigrade, and a voltage of approximately 1000 volts should be applied between the glass and the silicon wafer. The environment of such a high temperature and a high voltage does not cause a significant problem to the structure of the single crystal silicon, but when a controlling circuit is mounted thereon, it will lead to a destruction of a transistor. In other words, with the device formed by the anodic bonding, it is difficult to form mechanical MEMS components and a circuit to control thereof on the same substrate. Accordingly, the MEMS and the controlling IC have no choice but to be formed on separate semiconductors. Subsequently, an occupying area of the entire chip and the manufacturing cost are increased.
Moreover, the glass and the silicon wafer that have close thermal expansion coefficients need to be used. Therefore, a special glass is required in the anodic bonding, thereby causing problems of narrowing the choice of cap materials, and increasing the material costs.
With the capping method in Adit Decharat et al., Novel Room-Temperature Wafer-to-Wafer Attachment and Sealing of Cavities Using Cold Metal Welding, MEMS2007, pp. 411-414, because the concaves and the convexes are provided to the substrate and the cap material, and the respective concaves and convexes are fitted in, a load to the device is smaller compared with the anodic bonding. However, to correctly fit the respective concaves and convexes, the high alignment accuracy is required. Even if a small deviation occurs while fitting the substrate and the cap material, the concaves and the convexes will not fit properly, and may be joined diagonally leaving a space. Therefore, it is difficult to seal with high hermeticity.